1. Field of the Invention
The present invention relates to an electrochemical cell having a depletion gauge comprising an insulated resistive strip member which is positioned within the anode material of the cell and which is adapted to develop an increasing electrical resistance within the cell as the anode material is consumed, the increase in resistance serving to indicate the approaching end of life of the cell.
2. Description of the Prior Art
Heretofore, various electrochemical cells have been proposed which include depletion gauges which are adapted to indicate a decrease in voltage potential of the cell and the approaching end of life of the cell.
Examples of such previously proposed electrochemical cells are disclosed in the following U.S. patents:
______________________________________ U.S. PAT. NO. PATENTEE ______________________________________ 4,136,234 Fritts 4,388,380 DeHaan et al ______________________________________
The Fritts U.S. Pat. No. 4,136,234 discloses a charge sensing electrode for a primary battery which includes a sensing grid which is positioned within an electrochemical cell on or near the surface of a porous cathode within the cell and facing a separator and an anode within the cell. The voltage which is measured between the sensing grid and a cathode current collector grid is a function of the current distribution within the electrode which is continuously changing as the battery discharges, thereby indicating the state of charge of the cell.
The DeHaan et al U.S. Pat. No. 4,388,380 discloses a lithium cell having a depletion gauge which includes a lithium anode comprising two lithium plates wherein one of the lithium plates includes a stepped portion to thereby form a gap between the two lithium plates. A conductive sensing element is positioned within the gap and is in electrical contact with one of the lithium plates and is electrically insulated from the other lithium plate. An electrical potential which is developed between the conductive sensor and an outer conductive housing of the cell decreases to zero volts when the lithium plate in contact with the conductive sensor has become consumed to thereby provide an indication of a predetermined level of discharge of the cell.
Also in copending application Ser. No. 518,220 filed July 28, 1983 now U.S. Pat. No. 4,479,864 for: LITHIUM CELL HAVING CONTINUOUS DEPLETION GAUGE, there is disclosed a cell in which an elongate electrically resistive strip member is insulated on one side by an elongate strip of insulating material and is in contact on the other side with an anode material. The resistive strip member extends diagonally through the anode material and in a serpentine path between the upper and lower ends of the strip of insulating material such that as the anode material is consumed, a portion of the strip member is not in contact with anode material and is exposed to electrolyte. The greater the length of the exposed strip member, the more resistance in a sensing circuit, which serves to indicate the amount of discharge of the cell.
As will be described in greater detail hereinafter, the electrochemical cell of the present invention differs from the electrochemical cells previously proposed by providing a completely insulated resistive strip member which is positioned within the anode material of the cell and which is adapted to couple an increasing electrical resistance within the cell as the anode material is consumed. The resistive strip member includes a first layer of insulative material on a first major surface of the strip member and a second layer of insulative material on a second major surface of the strip member thereby to insulate the strip member from the anode material. The first layer of insulative material includes a plurality of passageways which contain conductive material therein that, upon exposure to an electrolyte as the anode material is consumed, has an electrochemical reaction with the electrolyte that forms a nonconductive layer and connects more electrical resistance of the strip member between the anode material and a conductor, the increase in resistance serving to indicate the approaching end of life of the cell.